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Comment by Thaxll | Hacker News Reader

I've seen Go code faster than Rust one, for example there was an interesting article years ago about counting words in a file:

https://benhoyt.com/writings/count-words/

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Yes, the default implementation of hashing in Rust is designed to be cryptographically-safe at the expense of speed. You can get a large speedup by replacing it, e.g. https://nnethercote.github.io/perf-book/hashing.html .

Maybe I'm still asleep, but can anyone who read this explain this part -

map[string]*int instead of map[string]int so we only have to allocate once per unique word.

I believe this is because the code `counts[word]++` basically works by:

    1. Hash word, retrieve the value from the counts map
    2. Increment the value
    3. Hash word, store the value into the counts map

By change counts to a map of strings to pointers of ints, you only need to perform #3 once per unique word. Once you've read the int pointer, you need only write to the pointer and not re-hash the word and write that to the map, which can be expensive.

https://github.com/benhoyt/countwords/blob/master/optimized....

Ah of course, the allocation is in the map setting work not the integer itself. That makes sense, thanks!

I am surprised this doesn't get optimized by the compiler. I assume this is necessary in the general case (map could be modified concurrently, causing the bucket for the key to move) but it obviously isn't here.

Anything nontrivial with a map in Rust is surprisingly tricky. I didn't know there were performance implications though.

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